2.2.2.6. Data Durability and Availability
š” First Principle: Data durability ensures information persists without loss; availability guarantees access during failures. Both are fundamental for data integrity and continuous business operations.
Data durability refers to the ability of data to remain intact and uncorrupted over its lifecycle, while data availability refers to the ability of users and applications to access data whenever needed. AWS designs its services with high inherent durability and availability.
Key Concepts:
- "Data Durability": Protection against data loss.
- Examples: Amazon S3 is engineered for 99.999999999% (11 nines) of durability by redundantly storing data across multiple devices and Availability Zones. Amazon EBS volumes are replicated within their Availability Zone.
- "Data Availability": Data is accessible when needed.
- Examples: Amazon RDS Multi-AZ automatically replicates data to a standby instance in a different Availability Zone, ensuring high availability and automatic failover. Amazon S3 also offers high availability.
- Strategies: Use backups, replication, and multi-AZ deployments.
Scenario: Storing critical application backups in Amazon S3 Glacier Deep Archive ensures long-term, highly durable, and cost-effective archival, protecting against data loss and enabling recovery for business continuity.
Visual: Data Durability vs. Data Availability
Loading diagram...
ā ļø Common Pitfall: Confusing durability with availability. S3 is highly durable (data won't be lost) but doesn't guarantee instant access during a major regional outage (that requires a separate DR strategy).
Key Trade-Offs:
- Higher Guarantees vs. Cost: Achieving higher nines of durability and availability (e.g., 11 nines for S3, Multi-AZ for RDS) inherently involves more redundancy and infrastructure, which translates to higher costs.
Reflection Question: How do architectural decisions regarding data durability and availability (e.g., using S3's 11 nines durability or RDS Multi-AZ) directly influence an application's overall resilience and recovery objectives (RPO/RTO)?